Spring Lake, a 101‐hectare impoundment that supplies potable water to Macomb, Illinois, was stocked with hybrid striped bass (striped bass Morone saxatilis ♀ x white bass M. chrysops ♂) from 1980 through 1985 at rates of 20‐30 fish/hectare. Fish from the 1982 stocking reached the 432‐mm minimum legal length in 28 months. Fish stocked when they were 20 mm long in June grew better and had higher survival rates than those stocked at larger sizes or later in the summer. Hybrid striped bass ate primarily gizzard shad Dorosoma cepedianum. Adult largemouth bass Micropterus salmoides, white crappies Pomoxis annularis, and channel catfish Ictalurus punctatus also relied heavily on gizzard shad, whereas juveniles fed mainly on invertebrates. Only white crappies showed any major seasonal change in food habits. By the end of 1985, white crappies were attaining a length of 200 mm 1 year earlier than in 1980. Numbers of white crappies and average sizes increased while fishing pressure and catches of other target species remained relatively unchanged. Some spillway loss of hybrids occurred.
Twelve hybrid striped bass (striped bass Morone saxatilis ♀ x white bass M. chrysops ♂) in 101‐hectare Spring Lake, Illinois, had temperature‐sensitive radio transmitters implanted in April and May 1985 to determine their temperature and oxygen preferenda. Tagged fish, which were monitored weekly from April 25 to September 30, 1985, ranged widely during most of the tracking period. Overall average movements were greater than 25 m/h 56% of the time. During summer stratification, however, fish concentrated in the deeper section of the lake between the old and new dams and moved only 27 m/h during this time, as opposed to 61 m/h before it. During stratification, the fish were confined to a narrow layer of water just above the zone of oxygen depletion, where water temperatures were consistently 2‐3°C cooler than near the surface. Fish appeared to prefer oxygen concentrations above 2 mg/L, which often forced them into water temperatures as high as 27°C.
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